Friction welding is a well-known process in which two components, moving relative to each other, are brought into contact under pressure and bonded at their interface. The motion at the weld interface may be rotational or non-rotational. Non-rotational motion includes linear, elliptical or vibratory motion. Friction welding by rotational motion typically requires at least one of the components be circular in cross-section. However, friction welding by non-rotational motion has received attention as a means of bonding components, where the weld interface of both parts is non-circular.
In non-rotational friction welding, one component is oscillated relative to the other component while a forge force is applied normal to the direction of motion. The motion is provided by a reciprocal motion assembly. The forge force moves the components into contact, and with metal components the friction between the components generates heat and plasticizes them. Once the motion stops, the metal solidifies, thus bonding the components.
One useful application of non-rotational friction welding is fabricating integrally bladed rotors for gas turbine engines. An integrally bladed rotor is a rotor assembly wherein the rotor blades are bonded directly to the rotor disk at spaced intervals about the circumference of the disk. In this way, individually manufactured components, each with selected properties, may be joined. The blades generally include a platform, an airfoil shaped midspan region extending from one side of the platform, and a stub region extending from the other side of the platform.
It will be appreciated that the conditions under which integrally bladed rotors are friction welded are stringent. In order to friction weld these components together the blades must be retained to the reciprocal motion assembly and firmly gripped with a holder (gripper). The disk must be held in a stationary position.
The blades are complexly shaped, therefore the gripper must have a compatible clamping mechanism. In addition, the blades may break relatively easily during welding, so the gripper must be able to support the blades in such a way as to minimize the likelihood of the blades breaking. Moreover, there are large forces associated with friction welding metal components. Typically, for metal components, the oscillation frequencies are less than about 100 Hz or cycles/second, depending on the part size and shape, and the forge forces are greater than 5000 lbs. force. Furthermore, numerous blades must be bonded to each disk within tight tolerances required for aerospace applications. Thus, the gripper must clamp tightly to withstand these forces and hold the blade so that the final position of the blade is accurate and repeatable consistently.
If the blade moves during welding, such movement risks damage to the friction welder. In addition, such movement risks not only misalignment of the blade being bonded, but misalignment of every subsequently joined blade. If misalignment is significant, the integrally bladed rotor cannot enter service, and will be scrapped or undergo costly reassembly. If misalignment is insignificant, the integrally bladed rotor may enter service but may have some resulting performance losses associated therewith. Furthermore, movement of the blade relative to the gripper is undesirable because any vibration of the blade absorbs energy and will increase the energy required to get proper oscillation of the blade.
Several possible grippers have been developed to hold the blades during friction welding. However, these prior art grippers fail to adequately meet the aforementioned needs. One solution is to form the blade within a solid stock of material, so that the blade remains integral with the block during bonding. In order to utilize this method the blade must be formed within a block of material by an expensive process and the block must be removed after joining. In a production environment it is faster and cheaper to manufacture the blades to their finished state and then join them to the disk.
Yet another solution is to form the blade with two holes therethrough. A U-shaped blade holder surrounds the midspan region of the blade and is bolted to the blade through the holes. The blade holder is then attached to the bonding machine. Using and removing this type of holder may be difficult where the geometry of the integrally bladed rotor requires the blades to be spaced closely together.
Another solution is to form the blade with a chamfered portion, and have the holder including a cavity and a clamping means with a chamfered end. When the blade is inserted into the holder the midspan region extends into the cavity, and the chamfered ends of the blade and holder mate. The chamfers of each element are such that when the clamping means is tightened its chamfered end forces the blade further into the cavity to minimize possible movement during welding. However using and removing this type of holder may be difficult where the geometry of the integrally bladed rotor requires the blades to be spaced closely together.
As a result of the above limitations of the holder discussed above, an improved gripper is sought, which holds the blade securely during subsequent friction welding to a rotor disk.